Heat-treatable platinum-gallium-palladium alloy for jewelry

ABSTRACT

A method of making jewelry comprising formulating a platinum alloy of at least 95 weight percent platinum, 1 to 5 weight gallium and palladium in an amount of less than about 3 weight percent, heat treating this alloy to increase the Vickers hardness by at least 20% but to not greater than a Vickers hardness of 350.

TECHNICAL FIELD

The present invention relates to platinum-gallium-palladium alloys whichare heat-treatable to high strength and hardness for use in jewelry, artobjects and related articles.

BACKGROUND ART

It is known in the jewelry-making art that the hardness and strength ofalloys can be increased by cold deformation. That is, it is known how towork gold and platinum alloys by various forging processes to harden andincrease yield strength to create stronger components, and for the useof exerting spring pressure. Increased strength is necessary for manytypes of durable structural parts such as lighter chains, pin stems, andthinner stampings. Spring pressure can be applied to form springcomponents for clasps, closures, wires, and springs. Even rings,pendants, bracelets, can mount center gemstones by compression springpower. The necessary pressure, in the latter examples, is supplied bythe springiness inherent in the structure of the worked precious metalmounting itself.

It is also known to those interested in the metallurgy of preciousmetals that many gold alloys and certain platinum alloys can be hardenedby heat-treatments to increase their hardness and yield strengths,sometimes even more than is possible through cold working. In thisregard, U.S. Pat. No. 5,084,108 discloses a heat-treatment process forincreasing the strength of certain alloys specifically for use ascompression-spring gemstone mountings.

Platinum is a precious metal and is relatively expensive. Platinum forfine jewelry is sold in high concentrations of over 90% and, by law,must be hallmarked accordingly. Platinum alloys are desirable for theirneutral color when combined with gems, they are hypo-allergenic, theyhave high tensile strength, and a pleasurable heft due to itshigh-density. In America, platinum alloys for jewelry manufacturingtraditionally have concentrations of over 90 percent platinum andcontain small amounts of iridium or ruthenium. There has been a recentintroduction of platinum-cobalt alloys for casting alloys that aresomewhat harder than the traditional iridium or ruthenium platinumalloys. Although work-hardenable, they are permanently softened by heatwhen soldering or using other metalworking techniques in jewelrymanufacturing. Platinum-cobalt alloys do not respond to heat-treatments.

U.S. Pat. No. 5,084,108 discloses certain heat treatable alloys ofplatinum containing 5 to 25% copper, 5 to 50% gold, 10 to 40% indium, 10to 70% iron or 7 to 35% silver. None of these alloys contain gallium orpalladium, nor is there any specific disclosure of hardness for theseplatinum alloys. Instead, that patent is primarily concerned with thestrengthening of certain alloys to provide compression spring mountingsfor gemstones.

Various gallium containing platinum alloys are known in the field ofmetallurgy. These alloys include 89-98.9% Pt, 1.1-11% Ga; 85-95% Pt,2-4% Ga, 3-12% Cu; 95% Pt, 2-2.5% Ga, 2.5-3% Au; and 95% Pt, 2-3% Ga,1-3% Au, 0-2.5 In. To the present inventor's knowledge, however, none ofthese alloys have been heat-treated to increase strength and hardnessfor use as jewelry components.

U.S. Pat. No. 4,165,983 discloses a number of different alloyingelements including palladium that can be used with platinum-galliumalloys, but is silent as to whether any heat treatments should beconducted on these alloys, despite a recognition that for many platinumjewelry applications, much harder metals (i.e., harder than 200 Vickers)are needed for use in the manufacture of springs and clasps. Thesolution to the problem of low hardness taught in this patent relates toa modification of the type and amount of alloying elements. Again, heattreatments are not used to increase hardness.

There are known heat-treatable platinum alloys such as 90% platinum-10%gold, but these alloys have undesirable characteristics for jewelrywork. A 90% Pt, 10% Au alloy tends to crack, is extremely difficult todraw into wire or roll, and does not cast well by known jewelry-makingtechniques. Platinum (90%+)/copper, used in Europe, does notsignificantly respond to heat-treatments, and only can be strengthenedby a few percent.

Due to the potential improvements in properties and performance of suchheat-treated alloys, there is a need for additional alloys that areheat-treatable for use in jewelry and art applications. The presentinvention provides one alloy family for this purpose.

SUMMARY OF THE INVENTION

The present invention relates to a method for making jewelry, whichcomprises formulating a platinum alloy of at least about 95 weightpercent platinum, about 1 to 5 weight percent gallium and an additionalalloying element of palladium in an amount effective as a propertyenhancing agent but in a total amount of less than about 3 weightpercent. This alloy is heat-treated to increase its initial Vickershardness by at least about 20% but to not greater than a Vickershardness of 350. Preferably, the alloy has an initial hardness of about150 to 200 and this is increased to about 250 to 325 after heattreatment. More preferably, the initial hardness is at least about 160and is increased to at least about 275. The heat-treated alloy hasparticular properties that render it useful as in general purposejewelry applications.

In this method, the two stage heat-treating operation may includesolution-treating the alloy at a temperature of at least about 1700 F.,quenching the solution-treated alloy to a temperature of below about 200F., and then, hardening the quenched alloy at at least 900 F. for asufficient time to achieve the desired hardness. Preferably, thesolution-treating temperature is at least 1800 F., the alloy is held atthat temperature for at least 10 minutes, and the solution-treating stepis conducted in an inert, non-oxidizing or anti-oxidizing environment.The solution-treated alloy is then quenched in water that is at roomtemperature or colder. Also, the hardening treatment is preferablyconducted by heating the alloy in an inert, non-oxidizing oranti-oxidizing gas atmosphere for at least 30 minutes at 1100 to 1200 F.The hardened alloy is then cooled to room temperature.

The alloy may be formed into a desired shape prior to the two-stageheat-treating operation. Such operations are many and include casting orfabricating. Some examples of fabrication can be by rolling of the alloyinto a sheet, drawing a wire, molding, casting, forging, stamping orconstructing the object or shape useful as a jewelry component. It isalso useful to process the hardened alloy to remove or prevent surfaceoxidation. One method to remove surface oxidation is by abrasion,although as previously mentioned, the alloy may be shielded during theheat-treating operations to prevent surface oxidation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention of this particular high-concentration platinum alloyhardened significantly by heat-treatment is extremely appropriate forthe manufacturing of jewelry, allowing for many advantages to thejewelry manufacturer over presently utilized alloys, such as:

1) Thinner, lighter constructions and castings, possessing significantlylowered weight and costs.

2) Springier clasps and mechanisms, not previously possible toconstruct.

3) Strengthening of delicate fabrications such as prong setting afterconstruction.

4) Higher polish, much easier to achieve, due to increased hardness.

5) Lower casting temperatures than previously known.

6) Lower costs with alloy additions other than traditional iridium orruthenium.

7) Expanded jewelry design possibilities.

The invention is preferably directed to platinum-gallium-palladiumalloys that can be cast to a desired form or worked by traditionalfabrication methods in an annealed state, then heat-treated andage-hardened to significantly increase their yield strengths so thatthey become hardened and spring-like. The alloys can be used for a widevariety of jewelry components, such as rings, clasps, spring parts, evencompression-spring settings for gemstones, and the like. These alloyscan be repeatedly annealed and heat-treated/age-hardened, and willactually increase in strength at room temperature over time.

As used herein, the term “age-hardening” is essentially synonymous withthe term “precipitation hardening” which results from the formation oftiny particles of a new constituent (phase) within a solid solution. Thepresence of these particles create stress within the alloy and increaseits yield strength and hardness. See, B. A. Rogers, “The Nature ofMetals”, p.320 (Iowa State University Press, 1964); H. W. Polock,“Materials Science and Metallurgy, p. 266 (Reston Pub. Inc. 1981) and“The Metals Handbook”, pp.1-2 (Am. Soc'y Metals, 1986).

A multitude of shapes or forms for the platinum-gallium-palladium alloysof the invention can be hardened by heat-treatments before beingutilized as jewelry. Mountings can hold stones by significantcompression-spring power.

In their annealed/softened state the alloys can be worked by standardjewelry-making techniques: they can be rolled, drawn, soldered to,shaped, bent, stamped, etc. These alloys can be applied to a variety ofdesigns for springs, gemstone mountings in rings, pendants, bracelets,chains, precious metal art objects, and the like.

It should be noted that in designing for structure of the jewelry or artobject, the smallest cross-sectional area and shape of a component istaken into account. It is possible to adapt the design of the alloy toalmost any configuration. The basic forms of these designs can vary,from simple sheet, to ring-shapes and more complex helixes, v-shapes,and the like. Objects can be wire, sheet, springs of all types,pendants, chain-links, brooches, and a multitude of others. Standardjewelry soldering techniques can be applied and repairs requiring heatcan be carried out. The alloys can be shaped, bent, built onto,annealed, and when the piece is done, the spring power and hardness canbe regained by heat-treatment. The alloy can be used to add durabilityto any jewelry component. Due to its superior hardness, its finish willalso last longer.

The hardness and strength of the alloys are increased by a simpleheat-treatment. The piece need not be forged to shape, like a coin isstruck, or a ring pounded on a mandrel with a hammer, etc. Rather, thepiece can be cast to any desired shape, or worked to its finished formbefore spring power or hardness is increased in it.

Not only does the technique of the present invention allow for morepossibilities than prior art work-hardening techniques for obtaininghardness or spring power, but the equipment involved is more economical.Instead of presses, dies, and drop-hammers to create spring power for aproduction of pieces, a simple electric furnace, hot oil bath, or thelike, is all that is required.

There are three basic steps when using construction methods to makecomponents of heat-treatable precious metal hardenable alloys accordingto the present invention. First, after the ingot is poured, the alloyshould be cold-work reduced in cross sectional dimension beforeconstruction is begun, that is, it must be rolled or drawn down (brokendown). Second, after the piece is constructed by standard jewelryfabrication techniques and is in its final form, the piece must becompletely solution-treated. Third, it must be hardened byheat-treatment in an oven for a certain amount of time (controlledprecipitation). It can then be cooled to ambient temperature.

In the case of as-cast shapes made of heat-treatable alloys, there aretwo basic steps to increase their spring power according to the presentinvention. After it is in its final form, the piece must first becompletely solution-treated. Second, it must be hardened byheat-treatment in an oven for a certain amount of time (controlledprecipitation). It can then be cooled to ambient temperature.

The invention is created by the addition of 1 to 5 weight percent of theelement gallium to platinum. Even additions of less then 3 percentgallium allow significant, beneficial hardening effects byheat-treatment. The addition of gallium in small quantities to platinumcosts significantly less than iridium or ruthenium and creates anunexpectedly unique and advanced product for jewelry manufacturing.

As too much gallium can cause excessive hardness, the present inventionrecognizes that palladium can be added as a diluent to ameliorate thehardness increases that occur during heat treatment without affectingthe desirable properties of platinum-gallium alloys. Furthermore, thepalladium addition imparts beneficial properties to the resulting alloy.

The examples demonstrate that the heat treatment of an alloy ofplatinum, 1-5% gallium, and 3% or less of palladium provides a materialthat is extremely useful for jewelry applications because of itscombination of desirable properties, including malleability, meltingrange, fluidity, hardness, resistance to oxidation, heat treatingability and cost. Also, tests were conducted to demonstrate thatplatinum alloys containing 1, 1.5 or 2.25% palladium and 4, 3.5 or 2.75%gallium, respectively, also possess the necessary balance of propertiesto be useful as a general purpose jewelry alloy. The most preferredalloy contains 95% platinum, 2.5% gallium and 2.5% palladium. It wasfound that this preferred alloy has the best overall blend of propertiesfor use in a variety of jewelry applications.

It is possible to add small or trace amounts of additional elements tothe platinum-gallium-palladium alloys of the invention. When addingcopper, cobalt, gold, iridium, silver, and/or indium, care has to betaken when selecting the maximum amount of the element or elements toinclude. Too much of those elements can result in increased oxidationwhen heated, reduced fluidity or adverse heat treating capabilities(i.e., too much or an insufficient response).

Testing has shown that such alloying elements, when used alone or incombination, have other beneficial effects on platinum-gallium-palladiumalloys, such as grain refining or adjusting the resulting alloy. Theadditional of less than one percent of iridium, for example, can act asa grain-refiner, reducing grain-growth. Small amounts (i.e., less than1%) of gold or cobalt are useful for increasing the fluidity of theresulting alloy, while similar amounts of gold or silver help fine tunethe heat treatability and iridium is beneficial as a grain reducer.Copper, cobalt, gold, iridium, silver and/or indium can be added toincrease the work hardenability of the final alloy. Additions of tracequantities of these elements vary the metallurgical structure andtherefore the characteristics of the alloy. Each of these elements canbe added in trace amounts provided that the total is less than about 2%by weight of the alloy.

The platinum-gallium-palladium alloy is preferably melted and blendedtogether by induction heating in appropriate crucibles for platinumalloys, and poured through water to create grain-shot than can be dried,weighed and used for casting.

Any forms made in wax can be easily cast by well-known traditionallost-wax casting techniques for platinum. Significantly, theseplatinum-gallium-palladium alloys cast easier than any other previouslyknown platinum alloy and are more energy efficient, due to theirrelatively low melting temperature. This lower temperature alloy alsoallows a lower mold temperature, decreasing defect rate due to shrinkageporosity, investment cracking, inclusions, and contaminations that occurmore readily at highly-elevated temperatures.

Ingots for sheet or wire fabrication can easily be cast by eitherinvestment lost-wax casting methods or into ingot molds for platinum.The alloy can be rolled to approximately a 30 to 40 percent reductionbefore needing an annealing procedure.

These platinum-gallium-palladium alloys are annealed at a temperaturearound 1800 F. by either furnace or torch to an orange-yellow, followedby an immediate quench in water.

There is slight surface oxidation that appears as a darkening or hazethat forms on the surface of this alloy during high-temperatureoperations and can be prevented by dipping the alloy inboric-acid/alcohol solution before bringing it to high temperature. Manyknown method for prevention of surface oxidation work well such asutilizing a shielding-gas or stainless-steel foil-wrap in combinationwith the boric-acid dip. Otherwise, the oxidation can simply be removedby abrasion with emery paper or polishes.

The hardening of this alloy is a two-step procedure. Solution-treatingis necessary previous to the hardening heat-treatment, to maximizehardening and its uniformity.

The alloy in cast form, in the form of sheet or wire stock, or in theform as a finished piece can be solution-treated at temperature near1800 F. in a furnace, preferably atmosphere-controlled withshielding-gas. Times vary for differing thicknesses. For an example,thirty minutes is an adequate amount of time for wire of over twomillimeters in diameter. The alloy must be immediately quenched in waterfrom the furnace.

The second heat-treatment, the hardening step of theplatinum-gallium-palladium alloy involves heating the piece atapproximately 1200 F. for a period of one hour in a furnace, preferablyatmosphere-controlled with shielding-gas. It can be allowed to air cooloutside the furnace.

The shielding gas can be any of the non-oxidizing inert gasses, such asargon, nitrogen, or mixtures thereof; anti-oxidizing gasses such ashydrogen, carbon monoxide, or “forming” or “cracked ammonia” gas(nitrogen with a few percent of hydrogen). The piece can also beprotected from oxidation by enveloping them with commercially availableheat-treating wraps.

EXAMPLES

The following examples illustrate the most preferred embodiments of theplatinum-gallium alloys of the invention.

Example 1

A 95% gallium, 5% gallium alloy was made and then cast into a wire. Asolution treatment of 1800 F. for 30 minutes under argon gas inconducted, followed by a quench into room temperature water. Next, ahardening step is conducted where the quenched alloy is heated to 1200F. for about 1 hour under argon gas. The alloy is then allowed to coolto room temperature. Vickers hardness measurements are taken on thismaterial after the solution treatment, and after the hardening step.These values are reported in Table 1. The hardening step raises theVickers hardness about 70%.

Example 2

The same alloy as in Example 1 is rolled to a flat strip before beingsubjected to the same solution treatment and hardening steps. TheVickers hardness measurements for this alloy is also shown in Table 2. Ahardness increase of about 75% is seen.

An increase in hardness implies an increase in strength and elasticity,as well as a reduction in ductility. Increases in hardness of at leastabout 25% to 50% are useful for many applications, although even higherincreases can be obtained as shown in these examples.

TABLE 1 Vickers Hardness (500 gm load) Alloy (Form) Range AverageHardness (HV) Cast-Solution Annealed 200-222 210 Cast-Hardened 340-385361 Rolled-Solution Annealed 204-385 213 Rolled-Hardened 350-384 374

Example 3

A platinum alloy for general purpose jewelry applications must have abalance of properties to be useful and accepted by the industry. Theseproperties include wear resistance, hardness, malleability, fluidity,melting point, oxidation resistance and cost. Table 2 presents acomparison of the properties of 99.9% platinum against alloys of 95%platinum-5% gallium (“95-5 alloy”), and 95% platinum-2.5% gallium-2.5%palladium (“95-2.5-2.5 alloy”).

TABLE 2 PERFORMANCE TESTS Wear Melting Amount of Material ResistanceHardness Malleability Fluidity Point Oxidation Cost 99.9 Pt Low SoftestVery High Low Highest Least High 95 Pt 5 Ga Very high Hardest Low HigherLow Most Lower 95 Pt 2.5 High Moderate High Highest High Low Lowest Ga2.5 Pd

Adding gallium to high purity platinum results in an alloy that is hardand can be heat-treated for even greater hardness. 99.9% platinum has anannealed Vickers hardness of 37 to 50, while that of the 95-5 alloy is200-222 and the 95-2.5-2.5 alloy is about 125-150. When the 95-5 alloyis heat-treated in accordance with the conditions of Example 1, itshardness is increased to a Vickers hardness of about 340 to 385. Thesame heat-treatment of the 95-2.5-2.5 alloy results in a Vickershardness of about 220 to 225. If gallium is used in an amount of morethat 5% and heat-treated according to Example 1, the resultingheat-treated platinum-higher gallium alloys have a Vickers hardness ofover 400 and are far too hard for use as general purpose jewelry alloys.This is so even when those platinum-higher gallium alloys are annealedand quenched to their softest state. The hardness of the platinum-highergallium alloy causes jewelry files to become dulled when the work isshaped before heat treatment.

In contrast, the 95-2.5-2.5 alloy has a relatively softer hardness whichenables the alloy to be shaped before heat treatment. Although it isharder that 99.9% platinum, the 95-2.5-2.5 alloy is readily workable.Wear resistance is related to hardness, with harder materials providinggreater wear resistance.

The results show that the 95-2.5-2.5 alloy has the best overall blend ofproperties for use in various jewelry applications ranging fromresilient spring clasps to malleable sheet stock which can be stamped orformed into shapes without tearing. The amount of oxidation presentafter a brazing or heat treatment operation is minimal and can be easilyremoved by conventional polishing to produce a lustrous surface. Thefluidity enables the material to be easily cast into desired shapes,while its high melting range enables repairs to be made withconventional platinum brazing materials without great concern ofdamaging the piece.

The fluidity of a jewelry alloy is related to its melting range and isimportant for casting quality. 99.9% platinum melts at about 1773° F.,whereas the 95-5 alloy has a melting range of about 1420 to 1610° F. and95-2.5-2.5 alloy has a melting range of about 1620 to 1685° F. The 95-5alloy begins to melt at too low of a temperature so that it is difficultto work on the alloy using standard brazing alloys without damaging thejewelry article. This is a concern when repairs need to be made to thearticle. The 95-2.5-2.5 alloy begins to melt at a higher temperature, sois less sensitive to this type of damage. Also, the melting range of the95-2.5-2.5 alloy compared to the 95-5 alloy enables the alloy to flowwell, particularly when used to cast and fill very fine forms or molds.

Regarding malleability, i.e., the ability of a metal or alloy to behammered or rolled, 99.9% platinum can undergo a percent reduction of 95or more before needing to be annealed. The annealing operation isnecessary to avoid defects such as cracks in the final article. Although99.9% platinum is very malleable, it is too soft to provide appropriatewear resistance. The 95-5 alloy being much harder, only can be reducedby about 30% before requiring an anneal, whereas the 95-2.5-2.5 alloycan be reduced by about 70% before an anneal is required. The 95-2.5-2.5alloy provides an unexpected increase by a factor of more than 2 inmalleability compared to the 95-5 alloy.

Although reducing the quantity of gallium in the platinum 5% galliumalloy can lower the hardness values, the cost of the alloy would beincreased as the proportion of platinum is increased. Also, the annealedVickers hardness would decrease due to the use of lower amounts ofgallium but only to about 190-200 (for use of 3.5% to 4% gallium).Furthermore, the malleability percent reduction would increase only toabout 44 to 55% for these alloys. The melting range would be about 1580to 1660° F. Also, these alloys oxidize to a greater extent thanplatinum-gallium-palladium alloys, so that platinum-gallium alloys arenot desirable for use as general purpose jewelry alloys.

The addition of palladium in amount preferably ranging about 1 to 2.5weight percent palladium to 95% platinum-2.5 to 4% gallium achieves abalance of properties so that the alloys are highly useful in generalpurpose jewelry applications. In addition, these palladium containingalloys are of lower cost. Specifically, it has been found that thesubstitution of palladium to replace some of the platinum or gallium ina platinum-gallium alloy enables the resultant alloy to have moredesirable hardnesses, fluidity, oxidation resistance and melting rangewithout increasing the platinum content and cost of the alloy.

Example 4

Additional tests were conducted to illustrate the usefulness ofadditional platinum-gallium-palladium alloys of this invention. Threealloys were made: each contained 95% platinum with Alloy A containing2.75% gallium and 2.25% palladium Alloy B containing 3.5% gallium and1.5% palladium and Alloy C containing 4% gallium and 1% palladium.Results are shown below in Table 3.

TABLE 3 PERFORMANCE TESTS Annealed Heat- Malleability Vickers treated %reduction Fluidity Melting Material Hardness Hardness* before anneal **Range Alloy A 125 160 65 high 1615 to 1670 Alloy B 188 268 55 high 1560to 1650 Alloy C 192 307 45 high 1565 to 1640 *per Example 1 **verycastable; fills fine forms easily and well.

The amount of oxidation of these alloys is comparable to 95-2.5-2.5alloy and better than platinum-gallium alloys having equivalent galliumcontents and is much easier to remove. Also, these alloys have arelative cost which is less than 99.9% platinum and platinum/gallium(alone) alloys having equivalent gallium contents and is comparable to95-2.5-2.5 and 95-5 alloys.

The foregoing examples are intended to illustrate typical improvementsin strength and hardness that can be obtained using the presentplatinum-gallium alloys and the novel heat-treatment process disclosedherein. Of course, higher or lower values can be attained by conductingroutine tests. Thus, it is understood that changes and variations can bemade in the foregoing without departing from the scope of the inventionwhich is defined in the following claims.

What is claimed is:
 1. A method for making jewelry, which comprises:formulating a platinum alloy of at least about 95 weight percentplatinum, about 1 to 5 weight percent gallium, and an additionalalloying element of palladium in an amount effective as a propertyenhancing agent but less than about 3 weight percent, said alloy havingan initial Vickers hardness; heat-treating the alloy to increase theVickers hardness by at least about 20% but to not greater than a Vickershardness of 350; and utilizing the heat-treated alloy as a component ofjewelry.
 2. The method of claim 1 wherein the heat-treating operationcomprises solution-treating the alloy at a temperature of at least about1700 F.; quenching the solution-treated alloy to a temperature of belowabout 200 F.; and hardening the quenched alloy at at least 900 F. for asufficient time to achieve the desired hardness.
 3. The method of claim2 wherein the solution treating temperature is at least 1800 F., thealloy is held at that temperature for at least 10 minutes, thesolution-treating step is an annealing step conducted in an inert, non-or anti-oxidizing environment, and the annealed alloy is quenched inwater.
 4. The method of claim 2 wherein the hardening heat-treatment isconducted by heating the alloy in an inert, non- or anti-oxidizing gasatmosphere for at least 30 minutes at about 1100 to 1200 F.
 5. Themethod of claim 4 wherein the hardened alloy is cooled to roomtemperature.
 6. The method of claim 1 wherein palladium content isbetween 0.5 and 2.5 weight percent, the initial Vickers hardness isbetween 125 and 200 and the final Vickers hardness is between 150 and300.
 7. The method of claim 1 further comprising adding one or moreproperty enhancing elements to the alloy in a total amount of no morethan 2 percent.